Tanning product and process



Patented May 10, 1949 UNITED STATES PATENT OFFICE TANNING PRODUCT AND PROCESS No Drawing. Application November 1, 1946, Serial No. 707,343

This invention relates to tanning and is more particularly directed to tanning compositions and tanning processes which employ a quinone-resorcinol polymer in the presence of a boron-oxygen radical.

Recently developed tanning processes which employ a quinone-resorcinol polymer as a tanning agent give excellent leather with a very high shrink temperature. For best results however this tanning agent must be used under mild conditions, such as are obtained by using dilute solutions and comparatively high pH. Penetration is not as rapid as could be desired and on some types of leather there is a tendency to grain drawing.

It is an object of this invention to provide tanning compositions and tanning processes employing a quinone-resorcinol tanning agent and securing improved penetration of skins and decreased grain drawing. It is a further object to provide tanning processes and compositions which are simple and economical to use and which have high effectiveness. Still further objects will become apparent hereinafter. The foregoing and other objects of this invention are attained by employing a boron-oxygen radical in conjunction with a quinone-resorcinol tanning agent.

Now before describing compositions and processes of this invention with more particularity, it will first be necessary to describe briefly the quinone-resorcinol tanning agents which are used as components of compositions of the present invention and which are used in tanning processes according to the present invention.

Simple addition products of quinone and resorcinol can be prepared by two techniques which both yield well characterized, low molecular weight, crystalline products.

1. By mixing quinone and resorcinol in equimolecular proportions without a solvent, heating, and distilling, a condensation product was obtained which has the structure of a mono-resorcyl hydroquinone:

teins. By the use of oxidizing agents it can be converted to mono-resorcyl quinone which is 6 Claims. (Cl. 8--94.24)

water-insoluble and therefore not adapted to use in tanning. The oxidized product has the for- 'mula:

2. By reacting quinone with an excess of resorcinol (molar ratio 1:5) at low temperature in 10% sulfuric acid, a crystalline precipitate is obtained which is diresorcyl quinhydrone; in other words, a complex comprising an equimolecular mixture of diresorcyl hydroquinone and diresorcyl quinone.

3. OH OH OH OH This crystalline complex is only slightly soluble in water and likewise has no tanning action on skins or precipitating action for proteins.

The quinone-resorcinol tanning agents recently developed are polymers unlike the compounds obtained by any of the procedures outlined above. They may be prepared by a preferred process, as explained more fully hereinafter, by refluxing the reaction product of quinone and resorcinol in excess of about a half an hour.

Quinone-resorcinol polymers for tanning ordinarily have more than about ten benzene rings per molecule and it is more specifically preferred to use polymers having from about twelve to eighteen benzene rings in the molecule. The products are further characterized by the fact that they contain an average of two oxygen-containing groups for each benzene ring.

The quinone-resorcinol tanning agents are Water-soluble, are amorphous, and are precipitated by acids. They are produced by processes under conditions which efiect polymerization. It

' can be observed also that the quinone-resorcinol polymers as described are tanning agents while those water-soluble compounds shown at the right in Formula 1 and in Formulas 2 and 3 do not serve as tanning agents.

In referring to the products as polymers of quinone with resorcinol it will be understood that the polymerization probably proceeds by the quinone first reacting with resorcmol, and the condensation product thus formed reacts either with similar units or with further quantities of quinone and resorcinol. The polymers are characterized accordingly by containing recurring units of a benzene ring substituted with two oxygen atoms in a para relationship, derived from quinone, and a benzene ring substituted with two oxygen atoms in a meta relationship, derived from resorcinol.

With further reference to the structure of the polymer it will be understood that the recurring six-membered rings which contain two oxygen atoms, as those in a para relationship derived from quinone, may be in a higher or lower state of oxidation as will be more particularly set out hereinafter. The oxygen may be present as a quinone-oxygen or as a hydroxy group. It is further to be observed that when comparatively larger proportions of quinone are used the polymer will be in a higher average state of oxidation.

Fortunately, the quinone-resorcinol tanning agents can easily be differentiated from the products as shown at the right in Formula 1 and in 2 and 3, and one is easily able to select those polymerization conditions which produce compounds best adapted for use according to the present invention. Quinone-resorcinol tanning agents, then, are prepared by eifecting polymerization of quinone and resorcinol, the conditions being sufiicient to produce a product which will precipitate gelatin, but which is not polymerized to such an extent that it is insoluble.

The polymerization of quinone with resorcinol may be carried out in any of the many ways generally well known to the art for effecting polymerization. The principal consideration in the ready selection of conditions for processes of preparing quinone-resorcinol tanning agents is to impose severe enough conditions that polymerization goes to a point such that the product is amorphous and will precipitate gelatin but not so severe as to result in the formation of an insoluble product. Those skilled in the art of effecting polymerization reactions will readily be able to suggest many specific procedures which will be suitable for preparing products to be used as tanning agents according to the invention.

The polymerization may suitably be effected, for instance, in an organic solvent such as acetone, methyl ethyl ketone, glacial acetic acid, ether-chloroform mixtures, acetone-chloroform mixtures, and cyclohexanone.

A catalyst such as a few drops of sulfuric acid or another acid such as acetic acid or hydrochloric acid is preferably included and, depending upon the other conditions selected, may be necessary to produce quinone-resorcinol products for use as tanning agents.

The polymerization may also be effected in various of the ways known to the art, but polymerization must not be so severe as to produce insoluble resins.

If the polymerization is eifected, as suggested above, in a suitable solvent, and with the use of a small amount of catalyst, the reaction may be permitted to proceed without the addition of heat until the exothermic reaction begins markedly to slow down. At this point heat is applied and the mixture refluxed for in excess of about, say, a half hour. The quinone-resorcinol product is then separated from the reaction mixture by removal of the solvent.

The term water-soluble is, standing alone, a little vague since many so-called insoluble materials are in fact soluble, at least to a certain extent. When the expression water-soluble is used herein it is intended to mean that the products are soluble in water to be usable as such in aqueous solutions and the solubility is, therefore, substantial. Generally it may be said that products can be designated water-soluble for the purpose of the present invention if, at 20 C., they are soluble to the extent of 10 grams per liter in water or slightly alkaline solutions of, say, pH '7 .5.

The ratio of quinone to the resorcinol is an important consideration in the preparation of compositions for tanning. Materials of ratios from 0.6:1 to 4:1 have been prepared and used in tanning. For tanning compositions of wide usefulness and variety of results there should be used a ratio of 1:1 to 3:1. It is to be observed that when such products are used as tanning agents they produce a leather having a shrink temperature above about F. For tanning compositions of greatest stability, however, it is much preferred that the quinonezresorcinol ratio be from about 1.5:1 to 2.5:1. Below and above these ratios the shrink temperatures fall off very rapidly while within these ratios the shrink temperature is'about 206 F. It will thus be seen that when the products are to be used as tanning agents for producing leather of very high shrink temperature, the narrower quinone resorcinol ratio is critical.

As has been observed above, quinone-resorcinol polymers for use as tanning agents may be in a higher or lower state of oxidation depending upon the precise conditions of preparation. An even greater variation in the state of oxidation of products produced as above may be effected by changing their state of oxidation by either treatment with an oxidizing agent or by treatment with a reducing agent.

A quinone-resorcinol tanning agent may, for instance, be treated with such oxidizing agents as hydrogen peroxide, potassium permanganate, persulfates, air, or oxygen, or any other of the common oxidizing agents. Leather tanned using such oxidized products is of a somewhat dark color by reason of the oxidation.

Generally it is not preferred to oxidize quinoneresorcinol tanning agents for use in tanning. It will also be noted that in the usual tanning operation there is considerable aeration of the solution and there may accordingly be some oxidation during the tanning process, tho this will be much less than would be obtained if an efifort were deliberately made to introduce air or oxygen. It will also be observed that instead of oxidizing the agents themselves before tanning, it is possible to oxidize the tanning solutions prior to or during tanning. Even after tanning is completed the finished leather may be treated with oxidizing agents tho this practice is not preferred.

Reducing of the quinone-resorcinol agents may similarly be efiected as by treatment with sodium bisulfite. As a matter of fact, it may even be found convenient to sell the products as bisulfite addition products. Leather prepared using an agent which has been treated with bisulfite has a "ilighter color .than that produced without the .use

.of reducing agents. Instead of using bisulfite, any other of the common reducing agents may be used, and there may be mentionedoxalic acid, .stannous chloride, or nascent hydrogen produced .as by the reaction of .zinc dust with acetic acid insitu. Reduction may also be effected .by catalytically reducing with hydrogen.

As with the oxidation, the reduction may .be effected during the tanning .or even may be applied to the tanned leather, tho such practices are not preferred.

For further detail on methods for making the 'quinone-resorcinol polymers employed in the compositions of this invention and for specific examples of the preparation of such polymers, reference should be had to :the copending Kirk application, Serial No. 664,428, filed April 23, 1946, which application claims the tanning compounds that .are obtained by the interpolymerization of .quinone and resorcinol.

According to the present invention, quinoneresorcinol tanning agents as described above are used with a compound vwhich supplies a boron- .oxygen radical.

Any compound may be used which can be dissolved in the tanning bath to yield in the solution boron-oxygen radicals. Thus any boron-oxygen compound may be used which is soluble in water to the extent of grams per liter at a pI-I of about 7 to 7.5. There may be employed, for instance, such soluble .boron compounds as boric acid (H3303) and alkali borates such as borai: (Na2B4O7-10H2O), sodium borate (NasBOc'), sodium perborates (NaBo3-H2O, NaBoa-zHzO), sodium metaborates (P1823204, NazB2O4-4H2O), and sodium tetraborate (NazBrOq, Na2B4Ov-5H2O).

Generally any soluble borate (including pyroborates and perborates) may be used and it will ordinarily be best to use the soluble alkali salts such as the sodium, potassium, or ammonium salts.

The boron-oxygen radical is believed to form a complex with the quinone-resorcinol polymer and .the amount of a compound containing the .boroneoxygen radical employed will depend in each case upon the magnitude of effect desired. Generally the amount of a compound containing the boron-oxygen radical should be such that there is about to 150 per cent by weight of the said compound based upon the weight of the .polymer. More specifically, it will ordinarily be preferred to use from-about 50 to 100 .per cent of a boron-oxygen-containing compound based upon the weight of the tanning agent used.

It will be understood that mixtures of compounds containing the boron-oxygen radical may be used. This will be found vparticularly desirable when the compounds selected have an effect upon the pH of the tanning solution. Thus by using a mixture of, say, borax and boric acid one may secure about the desired pH effect.

Compositions of the present invention may be prepared by incorporating in a solution of quinone-resorcinol polymers in acetone or, preferably, in water the desired compound which contains the boron-oxygen radicals. Alternatively, when a dry product is desired, the components to be used in making a tanning bath may all be mixed together in dry form.

It may also be found desirable to prepare an aqueous solution containing the polymer and the .desired amounts of compounds containing the boron-oxygen radical and drying the materials to produce a dry product. If .such a system is precipitated by the use of acid by bringing it, say, to about pH 3 to 4, there may be separated a product which .can be offered .as such. When .a .quinone-resorcinol polymer together :with borax in water solution are brought to a pH of about 13 to 4, a friable product is obtained which is readily dissolved in water at the pH of tanning.

In compositions of the invention the compound containing a boron-oxygen radical will amount to about 25 to 150 per cent, or preferably 150 to .per cent, by weight of the quinone-resorcinol polymer present. It will, of course, be understood thatsuitable .alkalies .or acids may be included .in such compositions for pH adjustment, though it will ordinarily be preferred to adjust .pH by suitable additions to the tanning liquor. It will also be understood that other tanning agents, wetting agents, and various tanning assistants may be incorporated incompositions of the present invention.

In order that the invention may be better understood reference should be had to the following illustrative example.

Example 1 A tanning solution was made up with 7.56 pounds of quinone-resorcinol polymer (15.2 pounds of a 50 per cent quinone-resorcinol polymer) dissolved in 56.7 pounds of water. To this was added 2.12 pounds of borax and 1.65 pounds of boric acid. The pH of the tanning liquor was 6.6 and sodium hydroxide was added to raise this to pH 7.0. Bated cowhides in the amount of 94.5 pounds (equivalent drained pickled weight) were placed in a tanning drum and the tanning liquor added. Drumming was continued for about 18 hours. Cuttings revealed that penetration was almost complete except for certain lean areas the heavier portions of the skin. A shrink temperature of 176 F. was obtained.

Drumming was continued for another two hours and then the pH was lowered over a six hour period to 5.5. Drumming was then continued intermittently during the next 12 hours. Examination of the skins at this time showed complete penetration, excellent grain character, and that the leather was well tanned.

Similar results were obtained by using formulations made up of a mixture of quinone-resorcinol polymer, borax, and boric acid in the proportions given above. The formulation was dissolved in the indicated amount of water to make up a tanning solution and the pH adjusted as above indicated.

Tanning of various types of skins was eifected in a manner similar to that above described but using difierent amounts of tanning agent. There were employed tanning solutions containing 1 to 20 percent of quinone-resorcinol polymer computed as solid polymer. In each of these borax or sodium borate or boric acid or a mixture of them was used in an amount equivalent to from about 25 to per cent by weight of the polymer present.

Example 2 Skin was first partially tanned by a procedure like that of Example 1. Retannage was effected by immersion of the treated skins in a solution of 60 per cent quebracho, 20 per cent oak bark, and 20 per cent chestnut extract containing 25 per cent tannin. The final leather was Well plumped, solid and of a pleasing brown color.

It is to be observed that the term skin is used generically to include heavy skins such as cowhide, lighter skins such as goatskins andcalfskins, and also skins of fur-bearin animals. It will naturally be necessary to adapt the processes to the type of skin to be treated. Those skilled in the art are well aware of such factors and may readily adapt the tanning agents of this invention to the needs of the particular tanning problem.

Skins to be tanned according to the processes of this invention may be prepared in any of the manners customary in the art, particularly for the preparation of skins for vegetable tanning. They may be unhaired, limed, delimed, and bated. The skins, if pickled, should be de-pickled before tanning for, as will be mentioned hereinafter, it is preferred to effect tanning under substantially neutral conditions. The skins may be given a salt-liquor treatment to soften them up and to render them of a more uniform condition as is the practice in the art.

While skins prepared in any manner may be treated according to the processes of this invention, it will ordinarily be desired that the skins be at a pH near 7, or slightly on the acid side. The tanning operation is conducted at about pH 6.5 to 7.5 and while the tanning solution may suitably be controlled to compensate for variance of the pH of skins, it will often be found advantageous to bring the skins to a suitable pH prior to introducing them into the tanning solution. Generally, it may be indicated that the tanning operation with the agents of the invention is conducted beginning at a pH of 6.5 to 7.5. The tanning is then finished off at a slightly lower pH ending up with a pH from about to 7.

The pH of tanning baths according to the present invention may be suitably adjusted by the use of conventional alkalies or acids and there may for instance be used such alkalies as alkali metal hydroxides or carbonates, and ammonium hydroxide. When it is desired to lower the pH of the tanning solution there may be used any acidic material such as lactic, hydrochloric, sulfuric, acetic, phosphoric, sulfamic, and formic acids.

Tanning processes, according to the present invention, are closely related to the vegetable tanning processes heretofore used and the close kinship between the processes makes it unnecessary to enter into great detail regarding tanning technique since those skilled in the art may use the tanning agents of the present invention in accordance with the practices already common in the art for vegetable tanning.

While the agents of the present invention may be used alone for tanning with excellent results, they may, if desired, be used together with any other tanning agent or tannin assistant known to the art. Again, in accordance with practices already well known, they may be used prior to or following other tannages. They may be used, for instance, in conjunction with vegetable tanning materials such as quebracho extract, with chrome tans, with synthetic tanning agents containing sulfonic acid groups, or with formaldehyde. They may also be used in conjunction with the tanning agents shown in the Graves Patents 2,205,832 and 2,205,883.

According to a preferred practice of the invention skins are first treated with a quinoneresorcinol polymer, as described above, and then finished oiT with a quebracho retannage. Similarly it is a preferred practice of the invention to tan first with chrome in accordance with practices known in the art and to finish off the tanning with a quinone-resorcinol polymer in the presence of 50 to per cent borax based on 1 to 20 per cent quinone-resorcinol polymer applied at pH 6.5 to 7.5.

The hides following treatment with a tannage of the present invention may be further treated with a soluble salt of aluminum, iron, titanium, copper, or chromium as in the Kirk Patent 2,205,901.

Leather produced according to the processes of this invention may be subjected to any of the various kinds of finishing treatments customarily used. The leather, if desired, may be suitably filled or given any of the numerous surface treatments customary in the art. Various of the soluble lignum products, many of which are byproducts of the paper-pulp industry, may also be used for the treatment of skins in conjunction with the processes above described. Such lignum products may, for instance, be introduced into the skins or leather and then precipitated in situ by a change of pH.

I claim:

1. A tanning composition comprising an interpolymerization product of quinone and resorcinol, the molar ratio of quinone to resorcinol being from 0.6:1 to 4:1, said polymeric product having more than four six-carbon (Cs) rings per molecule, having a ratio of about two oxygen-containing groups selected from the class consisting of quinone-oxygen and hydroxyl for each sixcarbon ring and being further characterized as water-soluble, amorphous, precipitated by acid, and able to precipitate gelatin; and the composition containing additionally about 25 to based upon the weight of the polymer, of a watersoluble, boron-oxygen compound selected from the group consisting of boric acid and an alkali borate.

2. A tanning composition comprising an interpolymerization product of quinone and resorcinol, said polymeric product being a solid containing at least ten six-carbon (Cs) rings per molecule, some of the six-carbon rings being obtained from quinone and containing in para relation two oxygen-containing groups selected from the class consisting of quinone-oxygen and hydroxyl for each such ring and substantially all the remaining six-carbon rings being obtained from resorcinol and containing two hydroxyl groups in meta relation, the ratio of the,firstmentioned rings to the second being 1:1 to 3: 1 and being further characterized as water-soluble, amorphous, precipitated by acid, and able to precipitate gelatin; and the composition containing additionally about 25 to 150%, based upon the weight of the polymer, of a water-soluble, boron-oxygen compound selected from the group consisting of boric acid and an alkali borate.

3. A tanning composition comprising an interpolymerization product of quinone and resorcinol, said polymeric product being a solid containing at least ten six-carbon (Cs) rings per molecule, some of the six-carbon rings being obtained from quinone and containing in para relation two oxygen-containing groups selected from the class consisting of quinone-oxygen and hydroxyl for each such ring and substantially all the remaining six-carbon rings being obtained from resorcinol and containing two hydroxyl groups in meta relation, the ratio of the first-mentioned rings to the second being 1.5:1 to 2.511 and being further characterized as Water-soluble, amorphous, precipitated by acid, and able to precipitate gelatin; and the composition containing additionally about 25 to 150%, based upon the weight of the polymer, of a water-soluble, boron-oxygen compound selected from the group consisting of boric acid and an alkali borate.

4. In a process for the tanning of skins the step comprising subjecting a skin to the action of a composition containing an interpolymerization.

product of quinone and resorcinol, the molar ratio of quinone to resorcinol being from 0.6:1 to 4:1, said polymeric product having more than four six-carbon (Cs) rings per molecule, having a ratio of about two oxygen-containing groups selected from the class consisting of quinone-oxygen and hydroxyl for each six-carbon ring and being further characterized as water-soluble, amorphous, precipitated by acid, and able to precipitate gelatin; and the composition containing additionally about 25 to 150%, based upon the weight of the polymer, of a water-soluble, boronoxygen compound selected from the group consisting of boric acid and an alkali borate.

5. In a process for the tanning of skins the step comprising subjecting a skin to the action of a composition containing an interpolymerization product of quinone and resorcinol, said polymeric product being a solid containing at least ten six-carbon (Cs) rings per molecule, some of the six-carbon rings being obtained from quinone and containing in para relation two oxygen-containing groups selected from the class consisting of quinone-oxygen and hydroxyl for each such ring and substantially all the remaining six-carbon rings being obtained from resorcinol and containing two hydroxyl groups in meta relation, the ratio of the first-mentioned rings to the second being 1:1 to 3:1 and being further characterized as water-soluble, amorphous, precipitated by acid,

and able to precipitate gelatin; and the composition containing additionally about 25 to 150%, based upon the weight of the polymer, of a, watersoluble, boron-oxygen compound selected from the group consisting of boric acid and an alkali borate.

6. In a process for the tanning of skins the step comprising subjecting a skin to the action of a composition containing an interpolymerization product of quinone and resorcinol, said polymeric product being a solid containing at least ten sixcarbon (Ce) rings per molecule, some of the sixcarbon rings being obtained from quinone and containing in para relation two oxygen-containing groups selected from the class consisting of quinone-oxygen and hydroxyl for each such ring and substantially all the remaining six-carbon rings being obtained from resorcinol and containing two hydroxyl groups in meta relation, the ratio of the first-mentioned rings to the second being 1.511 to 25:1 and being further characterized as water-soluble, amorphous, precipitated by acid, and able to precipitate gelatin; and the composition containing additionally about 25 to 150%, based upon the weight of the polymer, of a water-soluble, boron-oxygen compound selected from the group consisting of boric acid and an alkali borate.

HAROLD C. BEACHELL.

REFERENCES CITED The following references are of record in the file of this patent:

Pummerer et al.: Berichte, Dent. Chem. Gesel. vol. 60B, 1927, pages 1442 to 1448. 

